Sustained-release drug formulations for implantation

ABSTRACT

The present invention relates to a formulation for implantation having a novel constitution, which accomplishes controlled releases of active ingredients. The formulation comprises one of combinations (a), (b) and (c), as well as a carrier comprising a hydrophobic polymer, wherein the particle combination is dispersed into the carrier: (a) particles comprising an active ingredient, particles comprising a carbonate, and particles comprising a substance which is reacted with the carbonate in an aqueous solution to generate carbon dioxide (substance such as an acid); (b) particles comprising an active ingredient and a carbonate, and particles comprising a substance such as an acid; and (c) particles comprising a carbonate, and particles comprising an active ingredient and a substance such as an acid.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/07639 which has an Internationalfiling date of Oct. 31, 2000, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a sustained-release drug formulation,which is directed to long-acting effects of medicines and veterinarymedicines.

BACKGROUND OF THE INVENTION

Studies on sustained-release of active ingredients using hydrophobicpolymers as carriers of formulations to achieve long-acting effects ofmedicines, relief of side effects, decrease in frequency ofadministration, or the like, have been conducted. To controlrelease-rates of active ingredients is one of the most importantsubjects in these studies, and modifications of the form or thestructure of formulations, usage of additives, and so on, have beentried to attain the controlled release [U.S. Pat. No. 3,279,996,Contraception, 27(5), 483-495, 1983, Japanese Patent Publication (kokai)No. 45694/1980, Japanese Patent Publication (kokai) 174007/1987, WO9517881].

In case of the formulations for in vivo implantation containinghydrophobic polymers in which slightly soluble active ingredients aredispersed, the amount of the released active ingredients during adefined time period is smaller due to the low solubility of the activeingredients in the surrounding body fluid, and therefore, theformulations could not attain an acceptable efficacy of the activeingredients. With respect to such formulations as those containing theactive ingredients dispersed in the hydrophobic polymers, and decreasingin the release rate of the active ingredients, the methods forcontrolling the release rate of the active ingredients, which compriseusing, as an additive, mineral oil, glycerol, alcohol, or the like havebeen reported (Proceed. Intern. Symp. Control. Rel. Bioact. Mater., 14,223-224(1987), Proceed. Intern. Symp. Control. Rel. Bioact. Mater., 12,145-146(1985), and Japanese Patent Publication (kokai) No. 100315/1980).The key underlying these methods is to disperse an amphiphilic solventsuch as mineral oil, glycerol, or alcohol into the polymers togetherwith the slightly soluble active ingredients to ensure the solubilityand the released amount of the active ingredients to be increased.However, the formulations according to these methods may provide diverserelease rates, depending on a combination among the slightly solubleingredients, the additives, and the hydrophobic polymers, and,therefore, are limited to certain practical use.

In case of active ingredients such as live vaccines and inactivatedvaccines, which are neither soluble in an organic solvent nor in water,it has been unknown if the active ingredients could be released from thehydrophobic polymer.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a formulation for invivo implantation having a novel constitution which makes possible tocontrol the release rate of active ingredients.

We understood that the conventional methods for promoting the release ofthe active ingredient by increasing its solubility is limited to certainpractical applications, and have struck upon a new concept that in orderto accelerate the release of an active ingredient, a protruding forcephysically derived from the inside of the formulation is produced. Basedon the new concept, we continued to investigate, and accomplished thequite novel release-controlling technique, which is applicable tovarious cases in which sustained-release of active ingredients fromhydrophobic polymers is aimed. Specifically, the release-controllingtechnique comprises incorporating, into a hydrophobic polymer, particlescomprising a carbonate and particles comprising a substance which isreacted with the carbonate in an aqueous solution to generate carbondioxide, together with an active ingredient. The technique is applicableto any kind of active ingredients, and is especially useful for slightlysoluble, or insoluble ingredients.

The present invention provides:

(1) a formulation for implantation, which comprises one of particlecombinations, which is selected from a group consisting of (a), (b) and(c), as well as a carrier comprising a hydrophobic polymer, wherein theparticle combination is dispersed into the carrier:

(a) a particle combination which comprises particles comprising anactive ingredient, particles comprising a carbonate, and particlescomprising a substance which is reacted with the carbonate in an aqueoussolution to generate carbon dioxide;

(b) a particle combination which comprises particles comprising anactive ingredient and a carbonate, and particles comprising a substancewhich is reacted with the carbonate in an aqueous solution to generatecarbon dioxide; and

(c) a particle combination which comprises particles comprising acarbonate, and particles comprising an active ingredient and a substancewhich is reacted with the carbonate in an aqueous solution to generatecarbon dioxide:

(2) The formulation of item (1), wherein the active ingredient comprisesa slightly soluble, or insoluble ingredient.

(3) The formulation of item (2), wherein the insoluble ingredientcomprises a live vaccine, or an inactivated vaccine.

(4) The formulation of any one of item (1)-(3), wherein the hydrophobicpolymer comprises a polymer which is non-biodegradable.

(5) The formulation of item 4, wherein the hydrophobic polymer comprisessilicone.

When the formulation of the invention is administered to the body, thebody fluid infiltrates into the formulation to dissolve at least one ofthe particles comprising the carbonate and the particles comprising thesubstance which is reacted with the carbonate in an aqueous solution togenerate carbon dioxide, and induces the reaction between them, therebyleading to internal generation of the carbon dioxide gas from theformulation. The force for the gas to protrude toward the outside of theformulation accelerates the release of the active ingredients within theformulation. That is, the invention is applicable to an insolubleingredient, since the release rate is accelerated irrespective of thesolubility of the active ingredient in the body fluid according to theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 contains the results of Test example 2, and depicts a graph whichshows the decrease in the percentage of the remaining ivermectin in theformulations of the present invention, which were subcutaneouslyadministered to mice. Formulation 4 of the present invention wasprepared according to Example 4, whereas reference formulation 3 wasprepared according to Reference 3.

DETAILED DESCRIPTION OF THE INVENTION

More specifically, the present invention is characterized by the eventsthat (1) when the formulation is administered to the body, the bodyfluid infiltrates into the formulation to dissolve at least one of theparticles comprising the carbonate and the particles comprising thesubstance which is reacted with the carbonate in an aqueous solution togenerate carbon dioxide, and both are reacted so as to generateinternally the carbon dioxide gas from the formulation; and (2) thepressure force of the generated carbon dioxide gas puts the activeingredient dispersed in the formulation toward the outside, which eventsaccelerate the release of the active ingredients. Further, the gaspressure creates a fine crack within the formulation so thatinfiltration rate of water into the formulation increases, leading toaccelerating of the release of the active ingredients. Under thecircumstances, the invention is especially useful for slightly solubleingredients, of which release rate is slower, and insoluble ingredients.According to the invention, the pressure force which protrude the activeingredient toward the outside of the formulation, and the crackformation can be modified depending on an amount and a rate of thegenerated gas, by selecting a combination or contents between acarbonate and a substance which is reacted with the carbonate in anaqueous solution to generate carbon dioxide, and therefore, theinvention makes possible the control of the release rate of activeingredients.

As a preferred substance for “a substance which is reacted with acarbonate in an aqueous solution to generate carbon dioxide” used in acombination with a carbonate is an acid as described below, thesubstance may be abbreviated as “a substance(s) such as an acid(s)” ifnecessary.

An active ingredient, a carbonate, and a substance such as an acid whichare comprised in the formulation of the present invention can becombined in a manner of any one of the followings (a), (b) and (c):

(a) particles comprising an active ingredient, particles comprising acarbonate, and particles comprising a substance such as an acid;

(b) particles comprising an active ingredient and a carbonate, andparticles comprising a substance such as an acid;

(c) particles comprising a carbonate, and particles comprising asubstance such as an acid and an active ingredient.

In general, the carbonate is alkaline whereas the substance such as anacid are acidic. The combination thereof may be selected in light of pHstability of the active ingredient.

Particles comprising an active ingredient, particles comprising acarbonate, particles comprising a substance such as an acid) particlescomprising an active ingredient and a carbonate, and particlescomprising a substance such as an acid and an active ingredient(hereinafter, these are generally abbreviated as “particles comprisingan active ingredient, etc.”) may comprise solely the active ingredient,the carbonate, the substance such as an acid, the active ingredient andthe carbonate, and the substance such as an acid and the activeingredient, respectively, or they can include one or morephysiologically acceptable additive(s) such as an excipient, astabilizing agent, a solubilizing agent, a preservative, and a soothingagent.

Each of the particles comprising an active ingredient, etc., is notlimited to any particular species as long as it can be formed into asolid powder. The particles may be those which maintain the solid formin the formulation at a body temperature of animals (preferably mammals)or human to be administered. In particular, the particles preferablymaintain the solid form at the body temperature which is higher than thenormal temperature of animals or human by at least about 1° C., and whena disease to be treated is associated with a high fever, the particlesneed to maintain the particulate solid form at the much highertemperature than the normal temperature.

Specifically, the temperature which is higher than the normal bodytemperature of animals or human by at least about 1° C. is exemplifiedgenerally by 38° C. in case of the formulation to be administered tohuman, 43° C. in case of the formulation used in the human diseasesassociated with a high fever, 40° C. in case of the formulation to beadministered to animals (for example dog, cat, pig, cattle), and 45° C.in case of the formulation used in the animal diseases associated with ahigh fever.

The body temperature of animals is described in for example RINSHOKACHIKU NAIKA SHINDAN-GAKU (Rhoichi Nakamura, Yokendo, Japan, 1982), andit is possible to determine the minimum temperature to maintain thesolid form, referring to such documents.

Considering the body temperatures determined as shown above, theparticles comprising an active ingredient, etc., which maintain thesolid form at 50° C., could be applied to most animals or human.

Hydrophobic polymer is not limited to any particular polymer as long asit is biocompatible, and one of the hydrophobic polymers can be usedsolely, or in combination with one or more of other kinds of thepolymers. The hydrophobic polymers are roughly divided into anon-biodegradable and biodegradable polymers, and are exemplified by thefollowing, but are not limited to them. The non-biodegradablehydrophobic polymers include silicones, ethylene-vinyl acetatecopolymers, polyethylenes, polypropylenes, polytetrafluoroethylenes,polyurethanes, polyacrylates, polymethacrylates, and any others.Preferably, silicones, more preferably, Silastic® Medical Grade ETRElastomer Q7-4750 or Dow Corning® MDX 4-4210 Medical Grade Elastomer,and the like are employed. Biodegradable hydrophobic polymers areexemplified by polyesters, poly-amino acids, polyanhydrides, and thelike, including poly(lactic acid-glycolic acid)copolymers (PLGA),polylactic acids, and any others.

Carbonate is not limited to any particular species as long as it isphysiologically acceptable and is reacted with a substance such as anacid in an aqueous solution to generate carbon dioxide, and thecarbonate may be generally reacted in an acidic condition to generatecarbon dioxide. Specifically, carbonates are exemplified by sodiumhydrogen carbonate, sodium carbonate, potassium carbonate, potassiumhydrogen carbonate, ammonium carbonate, lithium carbonate, and the like,but not limited to them. Preferably, sodium carbonate, or sodiumhydrogen carbonate is employed. Any one of the carbonates can beemployed solely, or in combination with one or more other kind of thecarbonates.

Substance which is reacted with the carbonate in an aqueous solution togenerate carbon dioxide (substance such as an acid) is not limited toany particular species as long as the substance is physiologicallyacceptable and is reacted with the carbonate to generate carbon dioxide.Specifically, the substance includes an acid, and more specifically, itincludes, but not limited to, an organic acid such as citric acid,tartaric acid, malic acid, gluconic acid, fumaric acid, itaconic acid,phtalic acid, lactic acid, ascorbic acid, and an inorganic acid saltsuch as sodium dihydrogenphosphate, potassium dihydrogenphosphate, andan inorganic acid such as boric acid. It is preferable to employ citricacid or tartaric acid. Any one of the substances can be employed solely,or in combination with one or more other kind of the substances.

Either the carbonates or the substances such as an acid should bewater-soluble.

Active ingredient is not limited to any particular species as long as itis physiologically acceptable, and, it can be preferably slightlysoluble or insoluble according to the invention. Any one of the slightlysoluble or insoluble ingredients can be employed solely, or incombination with one or more other kind of the ingredients. Further, anycombinations of the slightly soluble and the water-soluble ingredients,or the insoluble and the water-soluble ingredients, or the slightlysoluble, the insoluble and the water-soluble ingredients can beemployed.

“Slightly soluble” as referred herein with respect to a ingredient meansthat the solubility of the ingredient in water is low, and, for example,the criteria that the solubility in water is “practically insoluble”(the amount of solvent required to dissolve 1 g or 1 ml of a solute is10,000 ml or more), “very slightly soluble” (the amount of solventrequired to dissolve 1 g or 1 ml of a solute is from 1,000 ml to 10,000ml), and “slightly soluble” (the amount of solvent required to dissolve1 g or 1 ml of a solute is from 100 ml to 1,000 ml), referring toJapanese Pharmacopoeia 13th revision (1996), may be used.

The slightly soluble ingredient is exemplified by antibiotics such asavermectin, ivermectin, and spiramycin; antibacterials such asamoxycillin, erythromycin, oxytetracycline, and lincomycin;anti-inflammatory agents such as dexamethasone, and phenylbutazone;hormones such as levothyroxine; corticosteroids such as dexamethasonepalmitate, triamcinolone acetonide, and halopredone acetate;nonsteroidal anti-inflammatory agents such as indomethacin, and aspirin;agents for treating artery occlusion such as prostaglandin E₁;anticancer agents such as actinomycin, and daunomycin; agents fortreating diabetes such as acetohexamide; agents for treating bonediseases such as estradiol. The active ingredients include not only anagent having a therapeutic activity, but also an agent having,supporting, or inducing a physiological activity, such as Vitamin D₃, oran adjuvant used in a vaccine, which includes hydrophobic adjuvants suchas muramyl dipeptide.

As “Water-soluble” as referred herein, the criteria that the solubilityin water is “sparingly soluble” (the amount of solvent required todissolve 1 g or 1 ml of a solute is from 30 ml to 100 ml), “soluble”(the amount of solvent required to dissolve 1 g or 1 ml of a solute isfrom 10 ml to 30 ml), “freely soluble” (the amount of solvent requiredto dissolve 1 g or 1 ml of a solute is from 1 ml to 10 ml), or “verysoluble” (the amount of solvent required to dissolve 1 g or 1 ml of asolute is less than 1 ml) according to Japanese Pharmacopoeia 13threvision (1996), may be used.

The water-soluble ingredient is exemplified by cytokines such asinterferons, and interleukins; hematopoietic factors such ascolony-stimulating factors, and erythropoietin; hormones such as growthhormone, growth hormone releasing factor, calcitonin, luteinizinghormone, luteinizing hormone releasing hormone, and insulin; growthfactors such as somatomedin, nerve growth factor, neurotrophic factors,fibroblast growth factor, and hepatocyte growth factor; cell adhesionfactors; immunosuppressants; enzymes such as asparaginase, superoxidedismutase, tissue plasminogen activating factor, urokinase, andprourokinase; blood coagulating factors such as blood coagulating factorVIII; proteins involved in bone metabolism such as BMP (boneMorphogenetic Protein); antigens which can be used in vaccines for humanand/or animals; adjuvants; cancer antigens; nucleic acids; antibodies;anticancer agents such as adriamycin, bleomycin, mitomycin,fluorouracil, peplomycin sulfate, daunorubicin hydrochloride,hydroxyurea, neocarzinostatin, sizofiran, sodium estramustine phosphate,carboplatin, phosphomycin, ceftiofur sodium, ceftiofur hydrochloride;antibiotics; anti-inflammatory agents; and alkylating agents. Theinterferons as referred herein may be α, β, γ, or any other interferonsor any combination thereof. Likewise, the interleukin may be IL-1, IL-2,IL-3, or any others, and the colony-stimulating factor may be multi-CSF(multipotential CSF), GM-CSF (granulocyte-monocyte macrophage CSF),G-CSF (granulocyte CSF), M-CSF (monocyte macrophage CSF), or any others.

“Insoluble” with respect to an ingredient means the property of theingredient which cannot be dissolved in water.

Examples of the insoluble ingredients include vaccines (live vaccine,inactivated vaccine) containing viruses or bacteria. The insolublesubstances include not only an ingredient having a therapeutic activity,but also an ingredient having, supporting, or inducing a physiologicalactivity, such as an adjuvant used in a vaccine, which adjuvanttypically includes aluminum hydroxide.

The formulation according to the invention can contain physiologicallyacceptable additive(s) such as a stabilizing agent, a solubilizingagent, a preservative, and a soothing agent. Further, the formulationcan contain an additive which controls the release of an activeingredient. The additive can be incorporated into a carrier, whether ornot the additive is added to the particles comprising the activeingredient, etc.

A process for preparing a particle combination comprising an activeingredient and a carbonate comprises, for example, making a homogeneoussolution of the active ingredient and the carbonate (an additive may beadded, if necessary), drying the solution to give a solid, and then, ifdesired, breaking up or sieving the solid. The drying method is notlimited to any particular method, and may be a drying method which isusually used in drying. The method typically includes a drying by a gasflow with nitrogen, helium, or air; a vacuum-drying; a freeze-drying;spontaneous drying; granulation; spray-drying by a spray-dryer; and aany combination thereof. Particles comprising an active ingredient and asubstance such as an acid can be prepared in a manner similar to theabove process. In the case that particles comprising an activeingredient, particles comprising a carbonate, and particles comprising asubstance such as an acid are separately prepared, the similar processcan be applied to the preparation for each particles.

BEST MODE FOR CARRYING OUT THE INVENTION

Release rate of an active ingredient in the formulation of the presentinvention can be controlled by the following factors:

(1) chemical or physical property of a carbonate, or a substance such asan acid;

(2) an amount ratio of a carbonate, and a substance such as an acid;

(3) an amount ratio of particles comprising an active ingredient, etc.and other additives in the total amount of the formulation;

(4) particle sizes of particles comprising an active ingredient, etc.,and particles of other additives; or the like.

When a carbonate is a stronger base, and when a substance such as anacid is a stronger acid, carbon dioxide gas is generated more vigorouslyduring a short time period. When the amount ratio of the carbonate andthe substance such as an acid is equivalent, carbon dioxide gas isgenerated most efficiently. Total amounts of the particles comprising anactive ingredient, etc. and the additives are not limited to anyparticular value as long as they can be dispersed into a carrier, andcan be formed into the formulation, and the total amounts of theparticles and the additives may be less than 70%, preferably less than50%, more preferably less than 30% by weight of the whole formulationalthough depending on chemical and/or physical property of the employedhydrophobic polymer. The content of the active ingredient naturally canbe varied depending on the species of the ingredient, the diseases to betreated, and the severity thereof. Particle sizes of the activeingredient, etc. are not limited to any particular size as long as thesizes enable the particles to be dispersed into a carrier and to formthe formulation. The sizes may be varied depending on chemical and/orphysical property of the used hydrophobic polymer, and are exemplified,for example, by 1,700 μm or less, preferably 500 μm or less, and morepreferably 300 μm or less in diameter. When the active ingredient isinsoluble, the particle size of the insoluble ingredient may be varieddepending on the particle sizes of the active ingredient, etc., andchemical and/or physical property of the used hydrophobic polymer, andthe particle size of the insoluble ingredient itself is exemplified by50 μm or less, preferably 20 μm or less, and more preferably 1 μm orless in diameter.

Shape of the formulation of the present invention may be selected fromany type of shapes as long as the formulation can be administered safelyinto living body, and particularly, include cylindrical, prismaticallycylindrical, cylindroid, tabular, and spherical shape. In case ofadministration with a needle, a cylindrical formulation is preferred. Incase of a cylindrical or tabular formulation, the side wall offormulation may be coated with an outer layer comprising only ahydrophobic polymer. In this case, the inner layer may be single, ormultiple. In case of the formulation having the multiple-layered innerlayers, the layers may be positioned to form concentric circles with asingle center, or may be positioned separately to form circles havingdifferent centers, in view of the cross section. Each of themultiple-layered inner layers may contain the same active ingredient, ordifferent ingredients. These shapes are particularly described in, forexample, Japanese Patent Publication (kokai) No. 187994/1995.

The formulations of the present invention can be prepared, for example,by mixing one of particle combinations which is selected from a groupconsisting of (a), (b) and (c), with a hydrophobic polymer beforecuring;

(a) a particle combination which comprises particles comprising anactive ingredient, particles comprising a carbonate, and particlescomprising a substance which is reacted with the carbonate in an aqueoussolution to generate carbon dioxide;

(b) a particle combination which comprises particles comprising anactive ingredient and a carbonate, and particles comprising a substancewhich is reacted with the carbonate in an aqueous solution to generatecarbon dioxide;

(c) a particle combination which comprises particles comprising acarbonate, and particles comprising a substance which is reacted withthe carbonate in an aqueous solution to generate carbon dioxide, and anactive ingredient: and

extruding the mixture through a nozzle, or molding the mixture. Curingmethod is exemplified by a polymerization process such as thepreparation of silicone, dissolution in an organic solvent and thesubsequent drying, such as the preparation of ethylene-vinyl acetatecopolymer, and the like. The outer layer and the inner layer may beprepared separately, or together. For example, a cylindrical formulationwith a single center in the cross section can be prepared by initiallypreparing an inner layer, then coating the layer with a liquidcontaining dissolved outer layer material, and drying them; or insertingan inner layer into a tube separately prepared from outer layermaterial; or molding an inner layer in a tube prepared from outer layermaterial; or simultaneously extruding inner and outer layers using anozzle. However, the preparation method is not limited to theseexamples.

For further descriptions of the present invention, the followingexamples and test examples are presented, but these examples and testexamples should not be construed to limit the scope of the invention.

EXAMPLE 1

A model for insoluble ingredients, fluorescence-labeled latex beads(Polyscience; 1 μm diameter) was washed with water, filtered with a 0.22μm filter, and dried in vacuo. An aqueous solution (3.63 g, 100 mg/ml)of citric acid and 60 mg of the fluorescence-labeled latex beads weremixed together, and the mixture was lyophilized. The lyophilized cakewas passed through a 300 μm-mesh sieve to obtain powder 1. Additionally,sodium hydrogen carbonate powder was passed through a 300 μm-mesh sieveto obtain powder 2. On the other hand, both 0.70 g of components A and Bof Silastic® Medical Grade ETR Elastomer Q7-4750 were mixed together,and immediately the mixture was kneaded together with 282.25 mg ofpowder 1 and 317.75 mg of powder 2. The kneaded material was filled in asyringe, extruded through a nozzle with a diameter of 1.6 mm byapplication of pressure, and allowed to stand at 37° C. for a day so asto cure. This was then cut to obtain formulation 1, of which shape iscylindrical (having a length of 10 mm and a diameter of 1.7 mm).

EXAMPLE 2

Fluorescence-labeled latex beads (Polyscience; 20 μm diameter) waswashed with water, filtered with a 0.22 μm filter, and dried in vacuo.An aqueous solution (3.63 g, 100 mg/ml) of citric acid and 60 mg of thefluorescence-labeled latex beads were mixed together, and the mixturewas lyophilized. The lyophilized cake was passed through a 300 μm-meshsieve to obtain powder 3. Then, both 0.70 g of components A and B ofSilastic® Medical Grade ETR Elastomer Q7-4750 were mixed together, andimmediately the mixture was kneaded together with 282.25 mg of powder 3and 317.75 mg of powder 2 prepared as in Example 1. The kneaded materialwas filled in a syringe, extruded through a nozzle with a diameter of1.6 mm by application of pressure, and allowed to stand at 37° C. for aday so as to cure. This was then cut to obtain formulation 2, of whichshape is cylindrical (having a length of 10 mm and a diameter of 1.7mm).

EXAMPLE 3

According to a method similar to that in Example 1, the kneaded materialcomprising the Silastic® elastomer containing the fluorescence-labeledlatex beads was prepared, and filled in a syringe. On the other hand,both 50 g of components A and B of Silastic® Medical Grade ETR ElastomerQ7-4750 were mixed together, and the mixture was filled in a secondsyringe. Nozzles having diameters of 1.6 mm and 1.9 mm were used toextrude both elastomers by application of pressure, which are assembledto form concentric circles with a single center so that thefluorescence-labeled latex beads-containing Silastic® elastomer waspositioned inside, whereas the Silastic® elastomer was positionedoutside. The resulting material was allowed to stand at 37° C. for a dayso as to cure, and then cut to obtain formulation 3, of which shape iscylindrical (having a length of 10 mm, a diameter of 2 mm, and an innerlayer diameter of 1.6 mm).

Reference 1

Both 0.98 g of components A and B of Silastic® Medical Grade ETRElastomer Q7-4750 were mixed together. Then, immediately the mixture waskneaded together with 40 mg of fluorescence-labeled latex beads(Polyscience; 1 μm diameter). The kneaded material was filled in asyringe, extruded through a nozzle with a diameter of 1.6 mm byapplication of pressure, and allowed to stand at 37° C. for a day so asto cure. This was then cut to obtain reference formulation 1, of whichshape is cylindrical (having a length of 10 mm and a diameter of 1.7mm).

Reference 2

Fluorescence-labeled latex beads (Polyscience; 1 μm diameter) was washedwith water, filtered with a 0.22 μm filter, and dried in vacuo. Anaqueous solution (8.4 g, 100 mg/ml) of glycine and 60 mg of thefluorescence-labeled latex beads were mixed together, and the mixturewas lyophilized. The lyophilized cake was passed through a 300 μm-meshsieve to obtain powder 4. Then, both 0.70 g of components A and B ofSilastic® Medical Grade ETR Elastomer Q7-4750 were mixed together, andimmediately the mixture was kneaded together with 600 mg of powder 4.The kneaded material was filled in a syringe, extruded through a nozzlewith a diameter of 1.6 mm by application of pressure, and allowed tostand at 37° C. for a day so as to cure. This was then cut to obtainreference formulation 2, of which shape is cylindrical (having a lengthof 10 mm and a diameter of 1.7 mm).

TEST EXAMPLE 1

Each of formulations 1 and 2 prepared in Examples 1 and 2, and each ofreference formulations 1 and 2 prepared in References 1 and 2 wasrespectively placed into 2 ml of phosphate buffer (pH 7.4) containing0.1% polyoxyethylene polyoxypropylene copolymer (ADEKA® Pluronic,Asahidenka Kogyo, Japan) and 0.01% sodium azide at 37° C., and the tubescontaining the formulation and the buffer were shaken gently. Theamounts of latex beads released from each formulation were determined bya fluorophotometer (excitation wavelength: 485 nm, emission wavelength:538 nm) in order to estimate the cumulative released amounts. Theseresults are shown in Table 1. Table 1 reveals that formulations 1, and 2according to the present invention accomplished acceleration of releaseof the latex beads, a model for insoluble ingredients, whereas referenceformulations 1 and 2 accomplished no or very little release of the latexbeads, showing the superiority in effect of the present invention.

TABLE 1 cumulative releasing formulation amounts for 15 days (μg/ml)formulation 1 32.4 ± 0.8 formulation 2 36.7 ± 3.2 reference formulation1  0.0 ± 0.0 reference formulation 2  0.1 ± 0.0

EXAMPLE 4

One hundred ten mg of ivermectin, 275 mg of sodium hydrogen carbonate,and 275 mg of citric acid, each of which had been ground, and passedthrough a 212 μm sieve, were thoroughly combined together. A portion(600 mg) of the combination was mixed with both 700 mg of components Aand B of Silastic® Medical Grade ETR Elastomer Q7-4750, and the mixturewas used as material for the inner layer. On the other hand, both 50 gof components A and B of Silastic® Medical Grade ETR Elastomer Q7-4750were mixed together, and the mixture was used as material for the outerlayer. An extruder (the bore of the outer nozzle: 1.9 mm, the bore ofthe inner nozzle: 1.6 mm), which accomplishes the extruding so that aninner layer can be covered with an outer layer in a manner of concentriccircles with a single center, was used to extrude the materials preparedas shown above. The extruded material was allowed to stand at 37° C. soas to cure, and then cut to obtain formulation 4, of which shape iscylindrical (having a length of 5 mm, a diameter of 1.9 mm, and an innerlayer diameter of 1.5 mm).

Reference 3

One hundred fifty mg of ivermectin, and 750 mg of sucrose, each of whichhad been ground, and passed through a 212 μm sieve, were thoroughlycombined together. A portion (600 mg) of the combination was mixed withboth 700 mg of components A and B of Silastic® Medical Grade ETRElastomer Q7-4750, and the mixture was used as material for the innerlayer. On the other hand, both 50 g of components A and B of Silastic®Medical Grade ETR Elastomer Q7-4750 were mixed together, and the mixturewas used as material for the outer layer. An extruder (the bore of theouter nozzle: 1.9 mm, the bore of the inner nozzle: 1.6 mm), whichaccomplishes the extruding so that an inner layer can be covered with anouter layer in a manner of concentric circles with a single center, wasused to extrude the materials prepared as shown above. The extrudedmaterial was allowed to stand at a room temperature so as to cure, andthen cut to obtain reference formulation 3, of which shape iscylindrical (having a length of 5 mm, a diameter of 2.0 mm, and an innerlayer diameter of 1.5 mm).

TEST EXAMPLE 2

Each of formulation 4 prepared in Example 4, and reference formulation 3prepared in Reference 3 was subcutaneously administered to mice. Theanimals were sacrificed under ether anesthesia on the analysing day, andthe administered formulations were recovered. The formulations wereplaced into methanol, and ivermectin dissolved in the methanol wasdetermined by a high performance liquid chromatography to estimate thepercentage of the remaining ivermectin in the formulations which hadbeen administered in the animals. The results are shown in FIG. 1.

FIG. 1 revealed that the percentage of the remaining ivermectin informulation 4 was decreased more drastically than that of referenceformulation 3, showing that the release of ivermectin from formulation 4was accelerated compared with that of reference formulation 3, and thusdemonstrating a superiority of the present invention.

EFFECTS OF THE INVENTION

As described above, the formulations for in vivo implantation accordingto the present invention provide controlled release rate of activeingredients on the basis of a protruding force physically derived fromthe inside of the formulation. The present formulations can be appliedto any active ingredients regardless of the kind of the activeingredients, and are especially useful for slightly soluble ingredients,or insoluble ingredients.

1. A cured sustained-release formulation for implantation, whichcomprises a carrier comprising a hydrophobic polymer and a particlecombination which comprises particles comprising an active ingredient,particles comprising a carbonate, and particles comprising a substancewhich reacts with the carbonate in an aqueous solution to generatecarbon dioxide, said particle combination being dispersed in thecarrier; wherein the active ingredient is either slightly soluble orinsoluble in water and the release rate of the active ingredient fromthe formulation is accelerated in a body fluid.
 2. A sustained-releaseformulation for implantation, which comprises a carrier comprising ahydrophobic polymer: and a particle combination which comprisesparticles comprising an active ingredient, particles comprising acarbonate, and particles comprising a substance which reacts with thecarbonate in an aqueous solution to generate carbon dioxide; saidparticle combination being dispersed in the carrier; wherein the activeingredient is either slightly soluble or insoluble in water and therelease rate of the active ingredient from the formulation isaccelerated in a body fluid; and wherein the particle combination isdispersed into the carrier, and wherein the formulation has a shapeselected from the group consisting of cylindrical, prismaticallycylindrical, cylindroid, tabular, and spherical shape.
 3. Thesustained-release formulation as claimed in claim 1 or 2, wherein theactive ingredient is an insoluble ingredient.
 4. The sustained-releaseformulation as claimed in claim 3, wherein the insoluble ingredientcomprises a live vaccine, or an inactivated vaccine.
 5. Thesustained-release formulation as claimed in claim 1 or 2, wherein thehydrophobic polymer comprises a non-biodegradable polymer.
 6. Thesustained-release formulation as claimed in claim 5, wherein thehydrophobic polymer comprises silicone.
 7. The sustained-releaseformulation as claimed in claim 1 or 2, wherein the active ingredient isa slightly soluble ingredient.